Basically any IRC client supports connecting to multiple servers simultaneously, so joining channels on multiple servers was never an issue. Also originally the "network" in IRC implied open federation just like you are describing, but over spam and moderation issues it evolved into a allow-list federation and ultimately incompatible s2s protocols. I sometimes wish people on the Fediverse would learn a bit more about the history of federated systems like IRC to avoid falling into the same traps 😅

As for your hidden comment number: there is currently a bug in Lemmy that shows message edits as new comments in the UI.